Recently, an electrophotographic organic photosensitive material having laminated layer comprising a charge generating layer and a charge transporting layer has been developed.
As a charge transporting material used for a charge transporting layer, various compounds such as pyrazoline compounds as disclosed in JP-B-37-16096 (the term "JP-B" as used herein means an "examined Japanese patent publication"), triarylamine compounds as disclosed in U.S. Pat. No. 3,180,730, stilbene compounds disclosed in JP-A-58-198043 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), hydrazone compounds as disclosed in JP-B-55-42380, oxadiazole compounds as disclosed in JP-B-34-5466, butadiene compounds as disclosed in JP-A-63-314554, etc., are known.
In these compounds, triarylamine compounds have been particularly noticed in view of high charge-transporting ability (mobility) and recently, various triarylamine compounds are proposed, e.g., in JP-A-1-280763, JP-A-2-178666, JP-A-2-178667, JP-A-2-178668, JP-A-2-178669, JP-A-2-178670, JP-A-2-190862, JP-A-2-190863, JP-A-2-230255, JP-A-3-78755, JP-A-3-78756, JP-A-3-78757, JP-A-3-114058, JP-A-4-133064, JP-A-4-193852, JP-A-4-312558, JP-A-5-19509, JP-A-5-80550, and JP-A-5-313386.
The triarylamine compounds can be synthesized by coupling reaction of an arylamine compound with arylhalide using a copper catalyst generally known. The arylhalide includes aryl bromide or aryl iodide. Of them aryl iodide is preferably used, since an aryl bromide shows a greatly low reactivity in the coupling (tertiary amine formation) reaction in the final stage.
These iodides of aromatic compounds can be synthesized by iodinating an aromatic compound with a sulfuric acid catalyst in a mixed solvent of water and acetic acid using iodic acid and iodine as shown in Ann., 634, 84(1960); by iodinating an aromatic compound with a sulfuric acid catalyst in a mixed solvent of water and acetic acid using periodic acid and iodine as shown in J. Chemical Society of Japan, 92, 1021(1971); or by a Sandmeyer reaction using a corresponding amino compound as shown in Bull. Soc. Chim., 7, 634(1940).
In the preparation of biphenylamine compounds disclosed in JP-A-1-280763, terphenylamine compounds disclosed in JP-A-2-190862, pyrenylamine compounds disclosed in JP-A-2-190863, fluorenylamine compounds disclosed in JP-A-2-230255, monoiodobiphenyl, monoiodoterphenyl, monoiodopyrene, or monoiodofluorene is used as an intermediate compound, which are synthesized by the same methods as described above. However, in synthesizing them by the Sandmeyer reaction, the corresponding amino compound which has a very strong toxicity has to be used, although the formation of a diiodo compound can be prevented. Whereby the compound must be treated with a specific care; the treatment after the reaction is complicated; and the yield of the compound is low, such a method being undesirable.
On the other hand, an iodination reaction with iodic acid or periodic acid is carried out with easy but the selectivity in a reaction to form a monoiodo compound or a diiodo compound is low, and thus the reaction product results in comprising a mixture thereof. When the amination reaction is carried out using the mixture containing the monoiodo compound and the diiodo compound, the reaction product after amination also comprises a mixture. Since impurities in the product provide harmful influences on the electrical characteristics of the charge transport material, a purification of the product is required. The molecular weight of these impurities is, however, considerably large not to be purified by distillation, etc., and thus a very expensive purification method such as a column purification, etc., must be used. In addition of expensiveness of iodine, a method accompanied by a formation of many diiodo compounds leads to a costly process in preparing arylamine compound.
Also, since in monoiodo compound and diiodo compound, the solubility of diiodo compound is greatly low, the diiodo compound can not be removed from the product by recrystallization which is simple in the industrial operation and has a large merit in cost. Therefore, for the product which contains about 10% or more of the diiodo compound, purification by distillation is required.
On the other hand, monoiodo compound has a high boiling point and a high melting point, and thus a high vacuum is required in the distillation of monoiodo compound, and the substance obtained by distillation is apt to be solidify to become difficult in handling. When the substance to be subjected to distillation contains a large amount of diiodo compound, in splashes to result in mixing of diiodo compound into the distilled substance by only a single distillation. Thereby, the purity of the product subjected to the single distillation is lowered. In this way, a fractional distillation is required in a purification of the product containing a large amount of diiodo compound, which causes complicated operation and excessive cost.
Also, it is described in Ann., 634, 84(1960) that by carrying out the iodination reaction in a saturated solution of an aromatic compound, the selectivity of monoiodo compound formation is increased. The method, however, does not provide a product having sufficient purity as a raw material used for a charge transporting material at low cost. Any process which will suffice for the above-described needs has not been found until now. The present invention is provided to solve the problems described above.